\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,decorations.markings,positioning, snakes}
% \usetikzlibrary{decorations.pathmorphing, patterns}
% \usetikzlibrary{calc, patterns, decorations.markings}
% \usetikzlibrary{positioning, snakes}

\begin{document}
\small
\begin{tikzpicture}[>=stealth,xscale=0.45]
  \draw [->](0,-2.5)--(0,2.5)node[right]{$y$ (\unit{cm})};
  \draw [->](0,0)--(20.8,0)node[right]{$t$ (\unit{s}) };
  \draw [very thick] plot[domain=0:6*3.1416, samples=1000] function{cos(x)} ;

  \foreach \x in {2,4,...,10}
  {
      \node at (\x/2*3.1416, 0)[below]{\x};
      \draw (\x/2*3.1416, 0)--(\x/2*3.1416, 0.15);
  }

  \foreach \x in {-2,-1,...,2}
  {
      \draw (0,\x)--(0.3,\x);
  }
  \node at (0,-2)[left] {$-10$};
  \node at (0,-1)[left] {$-5$};
  \node at (0,0)[left] {$0$};
  \node at (0,1)[left] {$+5$};
  \node at (0,2)[left] {$+10$};

  \draw (3.1416*4/2,1)--(3.1416*4/2,1.6);
  \draw (3.1416*8/2,1)--(3.1416*8/2,1.6);
  \draw (3.1416*6/2,-1)--(3.1416*6/2,-1.6);
  \draw (3.1416*10/2,-1)--(3.1416*10/2,-1.6);

  \draw [<->] (3.1416*4/2,1.3)--node[fill=white]{$T$}(3.1416*8/2,1.3);
\draw [<->] (3.1416*6/2,-1.3)--node[fill=white]{$T$}(3.1416*10/2,-1.3);
\end{tikzpicture}
\end{document}